An internal combustion engine injects fuel and air into a combustion chamber and burns the injected fuel and air, thereby generating power. When taking in air, the internal combustion engine operates an intake valve by driving a camshaft, and while the intake valve is opened, the internal combustion engine takes air into the combustion chamber. Further, by driving the camshaft, the internal combustion engine operates an exhaust valve, and while the exhaust valve is opened, the internal combustion engine exhausts air from the combustion chamber.
Currently, in order to improve fuel consumption of such a vehicle engine, research that applies cylindrical deactivation (CDA) is being performed.
In order to implement a CDA mode, by deactivating an intake/exhaust valve (VDA), a pumping loss can be minimized.
In general, when the CDA mode is implemented, intake valves or intake valves and exhaust valves of some cylinders are deactivated, and intake/exhaust valves of the other cylinders are activated.
FIG. 15 is a graph illustrating a valve profile when converting an operation mode of a general engine that can implement the CDA, and represents a profile of an intake/exhaust valve of a cylinder that is not deactivated.
In the drawing, K represents a profile of an exhaust valve, M represents a valve profile of an intake valve upon general operation, X represents top dead center, and Y represents bottom dead center.
When an engine load is changed from a high load to a low load, an operation mode of the engine is changed from a general operation mode to the CDA mode, and in order to increase an intake air amount, by moving closing timing of an intake valve to be adjacent to bottom dead center, an intake valve profile is moved from M to L.
In this case, as a valve overlapping segment in which an intake valve and an exhaust valve are simultaneously open increases, an internal EGR gas amount increases within a combustion chamber, and a knocking occurrence possibility increases due to a temperature increase of the combustion chamber and thus fuel consumption of the engine is reduced.
Due to such a phenomenon, there is a problem that an area of deactivation of some cylinders is limited.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.